In a known technology, when a predetermined sleep condition is fulfilled, a communication system transitions to a sleep mode limiting a function of each node to reduce power consumption of an overall system.
Further, there is known a method for transition of each node from the sleep mode to a wake-up mode in which the function limitation is removed. In this method, a wake-up signal is transmitted from a switch (relay device) using the same frame format as signals for ordinary communications between nodes are transmitted (refer to JP-A-2013-150346). In the above, the switch relays the signal to a transmission path to which the node is connected.
In the above technology, because the frame used for the wake-up signal is the same as those for ordinary communications, even after every node has transitioned to the sleep mode, the relay device has its all ordinary communication functions operable in order to process the wake-up signal. Because of this, the power consumption of the relay device cannot be reduced. The power consumption of the overall communication system cannot be sufficiently suppressed.